1. Field of the Invention
This invention relates to a device using an electrorheological fluid (hereinafter abbreviated as ER fluid simply) such as an ER fluid-filled engine mount, ER fluid-filled vibration damper, ER fluid-filled clutch, ER fluid-filled shock absorber, ER fluid-filled tension controller, ER fluid-filled composite material and the like, which are proposed in various industrial fields. More particularly this invention relates to a device using the ER fluid capable of sufficiently controlling power consumption and effectively preventing thermal runaway of electric current.
2. Description of the Related Art
An ER fluid reversibly and instantaneously generates a viscosity change in accordance with a value of a voltage applied. In this case, the voltage applied is high (generally several kV/mm), while the current density is very low (generally several .mu.A--several tens .mu.A/cm.sup.2), so that the power consumption required for controlling the viscosity of the ER fluid is small. Therefore, the application of the ER fluid to various control devices is actively forwarded.
In conventional devices using the ER fluid, the ER fluid is filled in a fluid enclosing space, while relative displacing passages of the ER fluid are defined in the fluid enclosing space and electrodes are disposed on the relative displacing passages.
For example, when the device having the above structure is considered as for use as a vibration damper, the viscosity of the ER fluid and hence the flow resistance of the ER fluid through the relative displacing passage can be changed in accordance with the voltage applied between the electrodes. As a result, the vibration damping force of the damper can properly be changed in accordance with frequency and amplitude of vibrations transmitted by adjusting the value of the voltage applied. Similar results are obtained in the other kind of the device.
In an conventional devices using an ER fluid, a low power consumption is maintained in a short time after the start of control, but a phenomenon of gradually increasing the power consumption is observed, and in extreme cases the control becomes impossible because the power consumption exceeds a capacity of a power source for the control.
That is, the electric current is passed to the ER fluid for controlling the viscosity of the ER fluid, so that Joule heat is created in the device. Furthermore, heat is generated by viscous flowing of the ER fluid. As the sum of these heat quantities exceeds the heat dissipating quantity of the device, the temperature inside the device gradually rises. As a result, there is caused a vicious circle that the rising of the temperature increases the current density and then the increase of the current density brings about a further rising of the temperature inside the device. In the worst case, thermal runaway of electric current (current density.times.electrode area) is caused.